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Many book shops, such as Foyles in London, opened at midnight to cope with demand

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Book fan Julia Stroud was the first in line to get a copy of Go Set A Watchman in a bookshop in Harper Lee's hometown of Monroeville, Alabama

Watchman contains some of the same characters as Mockingbird, including Scout and her father Atticus Finch. It has already proved controversial as early reviewers noted that Atticus expresses racist views in the story.

The story opens with Scout, now 26 and known as Jean Louise, returning on a train to her Alabama hometown from New York.

"It's making literary history to have a book that has a different take on characters that we've all grown to love," she said.

"I tried to read it simply on its own... There's some great storytelling in it."

Go Set a Watchman

2 million

initial US print run

70

countries released simultaneously

550 copies ordered by New York Public Library

7 translations available on day of publication

3 days wait for German translation

50% discount on RRP in many shops

AP

Publicity-shy author Lee, who is now 89 and lives in a nursing home in Monroeville, originally wrote the book in 1957, before reworking it with her editor to become courtroom drama To Kill a Mockingbird.

The story of racism and injustice in the fictional town of Maycomb in the American South went on to sell 40 million copies and be studied in schools around the world.

Mockingbird was also made into an Oscar-winning film starring Gregory Peck as lawyer Finch, who defends an innocent black man accused of raping a white woman.

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Media captionFans who queued for the midnight release explain why they are so excited for Harper Lee's new book

The existence of Go Set a Watchman was revealed in February and it is being released in 70 countries simultaneously.

The opening chapter of the novel was published for the first time on Friday, and many early reviews revealed that in later years Finch had in fact become "a bigot".

"This story is of the toppling of idols," wrote Sam Sacks in the Wall Street Journal, adding that it was "a distressing book, one that delivers a startling rebuttal to the shining idealism of To Kill a Mockingbird".

Sacks said: "For the millions who hold that novel dear, Go Set a Watchman will be a test of their tolerance and capacity for forgiveness."

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Harper Lee in 2007 when she was handed the Presidential Medal of Freedom

The New York Times said the revelation could "reshape Ms Lee's legacy" and made for "disturbing reading".

Writing for The Guardian, Mark Lawson said: "If the text now published had been the one released in 1960, it would almost certainly not have achieved the same greatness.

"This is not so much due to literary inferiority, but because Go Set a Watchman is a much less likeable and school-teachable book."

Lawson added that it was "in most respects, a new work, and a pleasure, revelation and genuine literary event... This publication intensifies the regret that Harper Lee published so little."

To Kill a Mockingbird

5,000

copies in initial print run

$20,000

value of a signed first-edition copy

Over 40m global sales

40 languages into which it has been translated

8 Oscar nominations for 1962 film version

3 Oscar wins

Getty

However, The Telegraph gave Go Set a Watchman a two-star review, with Gaby Wood writing "Harper Lee's editor deserves a Pulitzer for turning this ghostly first draft into the masterful To Kill a Mockingbird".

She added: "It feels like a sequel. But really, it's more like a ghost: The spectre of Lee's restless, ardent thoughts in progress."